Method of and means for making a current limiting fuse

ABSTRACT

A rectangular sheet of flexible insulation has metallic ribbons diagonally disposed thereon with the ends of adjacent ribbons aligned for juxtaposition when the sheet is formed into a cylinder and the ribbons form a helical fusible element for interconnecting end terminals of an enclosing insulating fuse housing.

United States Patent 1191 Foulkes Jan. 23, 1973 METHOD OF AND MEANS FOR 1 eferences Cited MAKING A CURRENT LIMITING FUSE 7 [75 1 Inventor: Fwlkes Elmhurst 3,317,691 5/1967 Bassani .337/159 [73] Assignee: S. & C. Electric Company, Chicago, ,0 9/1969 Curtis 338/308 1 3,486,155 12/1969 McCaughna... 337/295 3,611,241 10/1971 Herceg ..338 211 [22] Filed: March 13, 1972 Primary Examiner-Bernard A. Gilheany [2}] App! 234203 I Assistant Examiner-F. E. Bell Attorney-Robert R. Lockwood 52 us. c1. ..337/159, 337/290, 337/295,

' 338/207, 338/211, 338/308, 29/623 1571 ABSTRACT [5 Int. A rectangular sheet of flexible insulation has metallic 1 Field of Search ribbons diagonally disposed thereon with the ends of adjacent ribbons aligned for juxtaposition when the sheet is formed into a cylinder and the ribbonsform a helical fusible element for interconnecting end terminals of an enclosing insulating fuse housing.

14 Claims, 5 Drawing Figures METHOD OF AND MEANS FOR MAKING A CURRENT LIMITING FUSE This invention relates generally to thermally actuated switches and it has particular relation to current limiting fuses. It constitutes an improvement over the fuse construction disclosed in McCaughna U.S. Pat. no. 3,486,155, issued Dec. 23, 1969.

According to the patent above mentioned one or more silver ribbons are applied to a strip of flexible plastic material which then is wound about a ceramic core extending through a fuse tube having end terminals that are interconnected by the ribbon or ribbons. The fuse tube may be filled with sand and/orit may be evacuated. This construction is relatively expensive and difficult to assemble since the strip of flexible plastic with the ribbon or ribbons thereon is fragile and is difficult to apply to the ceramic core.

Among the objects of this invention are: To provide for making the current responsive element of a current limiting fuse that is relatively rugged in construction,

can be made with close manufacturing tolerances, can

be widely varied in cross-sectional dimension, and can be production-line tested before final assembly in a fuse housing.

According to this invention, diagonal sections of a fusible metal element are applied to one side or both sides a thin rectangular sheet of flexible insulating material with the ends of adjacent sections in alignment to permit their juxtaposition when the sheet is formed into a cylinder. The sections of fusible element are individually tested while still in a flat-sheet form. Then a cylinder is formed with fusible element sections either on the inside or outside of the cylinder or, for certain requirements, parallel sections of the element, for example, may be inside while other sections are on the outside of the cylinder.

Mechanical joining of the edges of the sheet in order to form the cylinder is by a suitable adhesive between the overlapped edges, by rivets, other suitable mechanical fastening devices, or by a combination of these devices. Electrical connection between sections of the fusible element is by electrically-conductive mechanical fastening devices, electronic welding, soldering, or by combinations of these devices. The completed cylindrical fusible-element assembly is tested for proper electrical and dielectric characteristics, encapsulated with the surrounding medium suitable for are extinction and cooling, such as sand, electrically terminated at each end for connection to an external circuit, and, finally, sealed in accordance with conventional fuse practice.

In the drawing,

FIG. 1 is a vertical sectional view taken generally along line 1-1 of FIG. 2 and shows the interior details of construction of a current limiting fuse embodying this invention.

FIG. 2 is a top plan view of the current limiting fuse shown in FIG. 1.

FIG. 3 is a horizontal sectional view taken generally along line 3-3 of FIG. 1.

FIG. 4 is a plan view of the rectangular sheet on which diagonal strips of metal are located in accordance with this invention.

FIG. 5 is a view of one of the diagonal strips having a different form of reduced cross section.

Referring now to FIGS. 1, 2 and 3 it will be observed that the reference character 10 designates, generally, a current limiting fuse in which this invention is embodied. The current limiting fuse 10 comprises a tubular insulating housing 11 provided with terminals, end caps or ferrules 12 at its ends. Connections 13 are provided for interconnecting the ends of a current limiting assembly, shown generally at 14, to the ferrules 12.

The current limiting assembly 14 is different from conventional current limiting fuse construction in that, as shown in FIG. 4, it is formed from a rectangular sheet 17 of flexible insulating material on which diagonal strips 18 of metal, such as silver, are located. The ends 19 and 20 of adjacent strips 18 are aligned so that, when the sheet 17 is formed into a cylinder, FIG. 3, with overlapping edge portion 21 secured by a suitable adhesive, such as epoxy, to the juxtaposed other edge portion, a cylindrical assembly is provided.

The rectangular sheet 17 may be formed of flexible glass having a thickness, for example, of from 0.0020 inch to 0.0300 inch. Such material may be a Micro- Sheet which is sold on the open market by Corning Glass Works. Other plastic material having both insulating and are extinguishing characteristics can be employed such as polytetrafluoroethylene.

The diagonal strips 18 of metal such as silver, having a thickness, for example, of 0.0016 inch and a width of 0.250 inch can be applied to the rectangular sheet 17 by a suitable adhesive and/or by the use of printed circuit techniques. After the ends of the rectangular sheet l7-have been overlapped, as indicated in FIG. 3, the juxtaposed ends 19 and 20 can be electrically interconnected by soldering 22, electronic welding or by rivets. A helical conductor is thus provided by the resulting cylindrical tube connected between the connections 13 to the terminals 12.

In accordance with conventional fuse practice, holes 23 are cut in the silver ribbon 18 and/or the rectangular sheet 17 in order to provide reduced cross sections of the fusible element. Alternatively, as shown in FIG. 5, notches 24 can be employed to provide the desired reduced cross sections. Additionally, and unlike what is economically feasible with a metallic ribbon or wire, the printed circuit technique permits the employment of holes, notches or other shapes which vary in size, shape, and spacing and widely-varied cross-sectional dimensions in order to attain arcing characteristics which are required for optimum performance of the fuse.

After the current limiting assembly 14 has been assembled in the insulating housing 11, it may be filled with granular material 25, such as sand, to imbed the diagonal strips 18 of metal therein in accordance with conventional current limiting fuse practice. Alternatively, the tubular insulating housing 11 and the terminals 12 can provide a hermetically sealed construction so that, after the assembly is completed, in lieu of the granular material 25, or in combination with the granular material 25, the interior can be evacuated.

With a view to removing heat from the current limiting assembly 14, openings 26 are provided in the end caps 12 along with an inner insulating tube 27, as shown in FIG. 3, through which air may circulate. When the tube 27 is employed, the space between it and the sheet 17 in tubular form is tilled with the granular material 25.

I claim:

1. A current limiting fuse comprising: an insulating housing, terminals at the ends of said housing, a tubular sheet of insulating material within said housing having longitudinal edges juxtaposed and secured together, diagonally disposed metallic ribbons on said sheet with the ends of adjacent ribbons juxtaposed, means interconnecting said juxtaposed ends of said ribbons to form a helical conductor between said terminals, and means interconnecting the ends of said helical conductor and said terminals.

2. A current limiting fuse according to claim 1 wherein said helical conductor is on the outer surface of said tubular sheet, and a filling of granular material in said housing embeds said helical conductor.

3. A current limiting fuse according to claim 1 wherein said housing is evacuated or is evacuated and partially filled with granular material.

4. A current limiting fuse according to claim 1 wherein said terminals have openings registering with the opening through an inner insulating tube to permit air circulation therethrough for cooling said helical conductor.

5. A current limiting fuse according to claim 1 wherein portions of said tubular sheet along said edges overlap.

6. A current limiting fuse according to claim 1 wherein said ribbons have various cross section areas corresponding to their current rating.

7. A current limiting fuse according to claim 1 I wherein said tubular sheet initially is a flat rectangular sheet having said ribbons formed on the surface or surfaces thereof.

8. A current limiting fuse according to claim 1 wherein said helical conductor is on the inner surface of said tubular sheet.

9. A current limiting fuse according to claim 1 wherein said helical conductor is on both surfaces of said tubular sheet.

10. Method of making a current limiting element for a current limiting fuse which comprises: on a rectangular insulating sheet applying in diagonal parallel relation metallic ribbons with the ends of adjacent ribbons in aligned relation, and forming the sheet into a cylinder with said ends in juxtaposition.

11. Method according to claim 10 wherein said metallic ribbons are on the outside of the resulting cylinder.

12. Method according to claim 10 wherein said metallic ribbons are on the inside of the resulting cylinder.

13. Method according to claim 10 wherein said metallic ribbons are on both the inside and the outside of the resulting cylinder.

14. Method according to claim 10 wherein said ends are electrically interconnected. 

1. A current limiting fuse comprising: an insulating housing, terminals at the ends of said housing, a tubular sheet of insulating material within said housing having longitudinal edges juxtaposed and secured together, diagonally disposed metallic ribbons on said sheet with the ends of adjacent ribbons juxtaposed, means interconnecting said juxtaposed ends of said ribbons to form a helical conductor between said terminals, anD means interconnecting the ends of said helical conductor and said terminals.
 2. A current limiting fuse according to claim 1 wherein said helical conductor is on the outer surface of said tubular sheet, and a filling of granular material in said housing embeds said helical conductor.
 3. A current limiting fuse according to claim 1 wherein said housing is evacuated or is evacuated and partially filled with granular material.
 4. A current limiting fuse according to claim 1 wherein said terminals have openings registering with the opening through an inner insulating tube to permit air circulation therethrough for cooling said helical conductor.
 5. A current limiting fuse according to claim 1 wherein portions of said tubular sheet along said edges overlap.
 6. A current limiting fuse according to claim 1 wherein said ribbons have various cross section areas corresponding to their current rating.
 7. A current limiting fuse according to claim 1 wherein said tubular sheet initially is a flat rectangular sheet having said ribbons formed on the surface or surfaces thereof.
 8. A current limiting fuse according to claim 1 wherein said helical conductor is on the inner surface of said tubular sheet.
 9. A current limiting fuse according to claim 1 wherein said helical conductor is on both surfaces of said tubular sheet.
 10. Method of making a current limiting element for a current limiting fuse which comprises: on a rectangular insulating sheet applying in diagonal parallel relation metallic ribbons with the ends of adjacent ribbons in aligned relation, and forming the sheet into a cylinder with said ends in juxtaposition.
 11. Method according to claim 10 wherein said metallic ribbons are on the outside of the resulting cylinder.
 12. Method according to claim 10 wherein said metallic ribbons are on the inside of the resulting cylinder.
 13. Method according to claim 10 wherein said metallic ribbons are on both the inside and the outside of the resulting cylinder.
 14. Method according to claim 10 wherein said ends are electrically interconnected. 